In this study, the numerical simulation of rolling process and experimental verification was carried out at 400℃ temperature of as-cast the AZ31 magnesium alloy sheet with initial thickness of 7mm. The reduction was 10%, 15%, 20%, 25%, 30%, 35%, 40% and 45%, respectively. Microstructure and edge crack were analyzed after rolling. The results show that the edge crack was occurred when the single pass reduction up to 20%. The edge crack depth has increased from 5.04mm of 20% reduction to 14.05mm of 45% in current rolling condition. According to numerical simulation results, the damage distribution along the width of the plate was obtained. And we have established the prediction model of edge crack depth. For the edge crack depth, the average error between the actual measured data and the calculated value by the prediction model is 9.23%. The SEM observation results show that the microstructure near the edge crack contain a large number of twins.